1. Field of the Invention
This invention concerns a fluid tank assembly capable of containing intermediate volumes of liquid in stacking relationship without additional reinforcement. More particularly, it is concerned with a tank which is rotationally molded of synthetic resin and wherein the walls of the tank are configured with corners including generally upright arcuate support portions to substantially retain the shape of the tank when filled, lifted from the bottom and/or stacked with similar tanks. The fluid tank assembly also has independent and removable support legs which facilitate stacking and retain a web-like bottom wall protector.
2. Description of the Prior Art
Various types of industrial liquids, including hazardous chemicals, are transported and stored in tanks and containers of a variety of sizes. These tanks have increasingly been manufactured of polyethylene or other synthetic resins for corrosion resistance, weight, and other reasons. These tanks have a storage capacity typically of from about 15 U.S. gallons to 793 U.S. gallons, and are often set on bases for lifting with a forklift. These bases underlie substantially the entire tank and may be complementally configured with the top of the tank as well as the bottom so that similar tanks and bases may be stacked one atop the other in the warehouse. Usually, such bases are separately attachable to the tank which contains the liquid.
Typically, these tanks have a specially designed shape and are formed with walls having a strong, rigid construction so that when several of the filled containers are stacked one on another, the container on the bottom of the stack has the load bearing capacity to support the total weight of the filled containers on top of it. Other types of containers have bases with stacking legs which surround the tank and extend above it, thereby protecting the tank and avoiding load transference through the walls of the tank. Among the tanks useful for transporting and storing industrial liquids are those shown in U.S. Pat. Nos. 5,490,603 and 6,079,580, both assigned to the assignee of the present invention.
Notwithstanding many beneficial features of these tanks, there remain several drawbacks. Tanks without stacking legs usually still require elaborate and expensive bases for stacking and dispensing liquid from the bottom outlet thereof, as well as to stabilize the tank and enable the tank to be lifted by a forklift. Moreover, in order to sustain the weight of filled tanks stacked thereon, the walls of the tank portion must be relatively thick and undamaged. Those fluid transportation and storage tanks having frames or stacking legs extending upwardly from their bases present significant advantages in terms of weight transfer, but are expensive to manufacture and may require the molding of three separate partsxe2x80x94the base and stacking legs, the tank, and the top protector.
Thus, there has developed a real need for an improved tank capable of handling industrial liquids, having good stacking characteristics with greater economy of manufacture. There is a further need for a tank having improvements in construction to maintain economy and still resist damage from fork lift tines and pallet jacks. There is additionally a need for improvements in the manner of elevating the bottom of the tank above a floor or other supporting surface.
These and other needs have largely been met by the fluid storage tank assembly of the present invention. That is to say, the invention hereof provides capabilities of storing intermediate amounts of liquid in a tank which is both self supporting and stackable when filled, and wherein the tank has very little deflection or dimensional difference between a filled and unfilled configuration. Furthermore, the tank avoids the need for a large base by employing legs which support the tank. The legs advantageously are removably mounted to the bottom wall of the tank, and retain an optional bottom protector in place in the manner of fasteners so that the protector acts as a shield between the bottom wall of the tank and pallet jacks or fork lift tines.
In greater detail, the assembly of the invention most preferably includes a tank and a plurality of removable support legs, and may also include a bottom protector of a relatively thin web of material which is held in position adjacent a bottom wall of the tank by the legs. The side walls of the tank are substantially curvilinear, with the tank including integrally molded support columns at its corners, whereby the tank presents a generally polygonal shape in horizontal cross-section. The support columns are integral with the side walls, receive liquid therein and thus, together with the side walls, top wall and bottom wall define the liquid receiving chamber. The preferred side walls are curvilinear rather than lying in flat, upright planes, and thus are somewhat arcuate either in vertical section, horizontal section, or possibly both vertical and horizontal section and merge into rounded corners along at least the top edge. The support columns are generally curved in horizontal section and may be generally of oppositely extending frustoconical portions or generally cylindrical in configuration. The support columns receive fluid therein and need not extend in a full circular in horizontal section but only a segment thereof, as the support columns are hollow to receive liquid as a part of the chamber formed by the support columns and the walls of the tank. The bottom wall preferably includes an integrally formed diagonally extending reinforcing channel extending from the center toward the support columns at the corner, with the top wall preferably similarly configured. The bottom wall adjacent the reinforcing channel is preferably somewhat arcuate whereby the reinforcing channel acts as a bottom support beam with the arcuate bottom wall to transfer the weight of the liquid carried within the tank to the support columns and to distribute the load to the vertical walls. The bottom deck of each of the ribs forming the reinforcing channel is substantially co-planar to provide an even engagement surface for facilitating lifting of the tank assembly by a fork lift or pallet jack. While the portions of the reinforcing channel atop the support columns are preferably flat and stepped downwardly relative to the top deck of the ribs of the reinforcing channel by an adjacent arcuate margin to provide reception surfaces for legs of a similar tank assembly stacked thereon, the reinforcing channel at the bottom of the support columns is preferably provided with internally threaded recesses to receive a threaded shank on the feet. In addition, the intersection of the diagonally extending ribs of the reinforcing channel is preferably indented in the top wall and a recess is threaded in the bottom wall to permit attachment of a leg thereto. The bottom wall of the tank is preferably provided with an outlet threaded to receive a pipe or valve thereon, while the top wall may include a threaded collar to receive a cap and a threaded internal neck for mounting of a bung. The tank is preferably made by rotational molding of polyethylene or other suitable synthetic resin.
The legs are also molded of polyethylene or other synthetic resin, either by blow molding, rotational molding or injection molding. The legs are provided with a shoulder for retaining the bottom protector in position and a threaded shank sized and threaded complementally to the recesses in the bottom wall of the tank.
The optional bottom protector is configured for positioning beneath the bottom wall of the tank and includes openings therein sized to receive the shanks of the but abut the shoulders of the legs. The bottom protector is a relatively thin web or sheet of material which helps avoid damage to the bottom wall and distribute force from the fork lift tines to the reinforcing channel. Thus, the legs serve the dual purpose of elevating the tank above the floor and holding the bottom protector in position.
In use, a plurality of tanks may be stacked one atop the other, even when filled. The bottom surface of the legs of the upper tank assembly rest on and are held in position by the margins or rims on the diagonally extending reinforcing channel in the top wall. Because each of the support columns and the center indentation in the reinforcing channel are recessed below the channel and face outwardly from the center, the upper tank may be readily lifted off the lower tank but resists lateral movement relative thereto. The arcuate configuration of the sidewalls and the integrated support columns cooperate to bear the load of the tank as well as assemblies positioned thereon. Pallet jacks or fork lift tines are provided ready access because the legs elevate the bottom wall and the bottom protector above the floor, and the bottom protector, which may be readily replaced, helps to isolate the bottom wall of the tank from damage caused by the pallet jacks or fork lift tines.
These and other advantages will be readily apparent to those skilled in the art with reference to the description and drawings presented herewith.